1. Field of the Invention
This invention relates to a method and an apparatus for peeling a coating from coated plastics in a simple and effective manner. This invention also relates to a method for recycling plastics utilizing the above method and apparatus, which can provide recycled plastics at a low cost in a pollutionless manner without entailing a considerable lowering in the properties of the recycled plastics.
2. Background Art
Used plastics have hitherto been burned in an incinerator or buried together with other wastes under the ground. Combustion of such plastics increases carbon dioxide concentration in the air, leading to the serious problem of global warming. When they are buried under the ground, they cannot be decomposed by microorganisms and hence remain as they are, so that the amount of the plastics accumulated under the ground increases year by year.
In recent years, recycling of plastics has been advocated from the viewpoint of resource conservation and the earth's environmental protection.
However, various difficult problems should be solved in order to successfully recycle used plastics.
One of such problems is related to the fact that plastics as final products often are a composite of dissimilar materials, rather than a product of a single material. When such plastics as a composite are recycled without separation of the dissimilar materials, the recycled products often have inferior mechanical properties and appearance to those of the original plastics.
For example, when a coated plastic product, as such, is pulverized, repelletized with an extruder, and remolded by means of a molding machine into a recycled plastic product, the coating which has been formed on the surface of the original plastic product remains in the recycled plastic product without being finely dispersed therein. Since the coating that cannot be finely dispersed inhibits homogeneous blending of resins, the properties of the recycled product is considerably lowered.
Therefore, it is of most importance to remove a coating from a coated plastic product in advance of its reprocessing for recycling. To this end, the following methods may be considered or, have been proposed in the art.
1 A method may be considered wherein a coated plastic product, as it is, is fed to an extruder, where the coating material which does not melt is removed by filtration through a screen such as a metal gauze. In this method, however, clogging of the screen will lower the throughput, resulting in a lowering of the production efficiency. Further, since the coating material cannot be effectively removed, no good recycled product can be obtained.
In order to minimize the lowering of production efficiency due to clogging of the screen, the provision of an equipment for automatic filter replacement and an increase in filtration area may be considered. With these countermeasures, however, the method is still deemed unsatisfactory.
2 Japanese Patent Application Laid-Open No. 93157/1993 discloses a method wherein a large amount of a strong alkali is used to hydrolyze the coating of a coated plastic product. This method requires an additional equipment for waste water disposal.
3 Swelling of the coating of a coated plastic product using an organic solvent followed by peeling-off of the coating may be considered. This method will involve a great expense for the recovery of the solvent. Further, there is a fear of environmental pollution due to the use of the organic solvent.
4 Japanese Patent Application Laid-Open No. 273207/1990 proposes a method wherein a coating of a coated plastic product is removed by blasting with a soft abrasive material.
According to this method, when the shape of the coating surface is complicated, the blasting efficiency is low and the coating cannot be sufficiently removed. Further, this method is not suited for continuous treatment of coated plastic products having different shapes.
5 Japanese Patent Application No. 192431/1991 proposes a method which comprises heating a coated plastic product in the presence of water or an organic solvent, such as an alcohol, to a temperature of the melting point of the plastic or below or to a temperature above the melting point of the plastic thereby to hydrolyze the coating material, and then melting and kneading the plastic product to disperse the decomposed coating therein. The hydrolyzing treatment additionally requires the steps of waste liquor disposal and of drying after the treatment, resulting in an increased treatment cost. In addition, since the decomposed coating material is finally included in the recycled product, the properties thereof are likely to be lowered.
6 Japanese Patent Application Laid-Open No. 337941/1993 discloses an apparatus for peeling a coating from a coated plastic product.
This peeling apparatus, as shown in FIGS. 7 and 8, is so constructed that a plastic product, for example, a side moul 22, is carried by a pair of carrying rollers 21 into between rotators 23 and 24 each made of a synthetic resin foam, the carrying speed V of the side moul 22 being adjusted to be lower than the rotational peripheral speed of the rotators 23 and 24 so as to apply cutting and high frictional forces to a coating 22a and a double face adhesive tape 22b on the surfaces of the side moul 22, thereby cut-peeling the coating 22a and the double face adhesive tape 22b, and the side moul 22 is delivered outside the system by means of the pair of carrying rollers 21.
In the case of this apparatus, since a resin product is brought into contact with rotators 23, 24 each made of a synthetic resin foam, the rotators are subject to brittle fracture, which will generate dust and worsen the working environment. Further, this apparatus is unsuitable for use with bent or curved plastic products.
It is therefore an object of the present invention to provide a method and an apparatus for effectively removing a coating from coated plastics at low cost and in a pollutionless manner.
It is another object of the present invention to provide high-quality recycled plastics by utilizing the above method and apparatus.